The present invention relates to graphics drum plotters and, more particularly, to a graphics drum plotter creating virtual columns on the strip paper and placing the plots across the strip in the columns before advancing the strip so as to employ the entire paper width.
A typical prior art drum plotter is shown in simplified form and generally indicated as 10 in FIG. 1. The plotter 10 has a beam 12 disposed parallel to and spaced from a drum 14. The drum 14 has sprockets 16 along both edges adapted to mate with holes 18 in strip paper 20. A writing head 22 carrying a pen 24 is mounted on the beam 12. Under the control of output logic 26 connected thereto the drum 14 is rotated to move the paper 20 under the writing head 22 and pen 24 and the writing head 22 is moved back and forth on the beam 12 so as to create a series of plots 28 on the strip paper 20 reflecting X and Y coordinate contained in the output signals from the output logic 26. Typically, the strip paper 20 passes into a pair of vacuum columns, such as that generally indicated by the area 30, adjacent the drum 14 so as to prevent undue stresses on the strip paper 20 as the drum 14 is rotated and quickly reversed in direction during the plotting process.
As can be seen in the example of FIG. 1, if the series of plots 28 are small in size, a sequence of plots 28 will be created along one edge of the strip paper 20 with the balance of the strip paper 20 being wasted. As shown in FIG. 2, the alternative has been to replace the drum 14 with a shortened drum 32 which also requires the placing of a baffle as at position 34 within the vacuum columns 30 so as to properly draw the narrower strip paper 20 then employed therein. Obviously, such a changeover procedure between narrow plots and wide plots is both time consuming and bothersome. Wherefore, it is the object of the present invention to provide a system for efficiently using wide paper and its associated drum in producing small plots.